Maillard Reaction

Celebrating the centennial of a landmark in culinary chemistry

Baked bread, roasted coffee, and grilled steak owe their enticing smell to a sequence of chemical reactions that was first reported 100 years ago by the French chemist Louis-Camille Maillard.

His 1912 paper took a first stab at explaining what happens when amino acids react with sugars at elevated temperatures, and in doing so, Maillard set the foundations of serious food science (Compt. Rend. 1912, 154, 66).

Although it is responsible for some of cooked foods’ more delightful flavors as well as the brown color of bread crusts, soy sauce, and barbecued meat, the Maillard reaction also has a dark side: It can produce cancer-causing acrylamide and furans in food, particularly highly processed or burnt meals. Medical researchers have also discovered that the Maillard reaction takes place spontaneously in human tissue, and its products have been linked to a variety of diseases, including diabetes and cataracts.

“The Maillard is, by far, the most widely practiced chemical reaction in the world,” said chemistry Nobel Prize winner Jean-Marie Lehn late last month in Nancy, France, some 20 miles from the village of Pont-à-Mousson, where Maillard was born. That’s because the reaction takes place daily in households around the globe whenever food is cooked, Lehn told the group of 270 international scientists who had gathered on Maillard’s home turf to honour the reaction’s centennial and attend this year’s International Maillard Reaction Society conference.

Prior to Maillard’s paper in 1912, which described the reaction between reducing sugars and amino acids, “there wasn’t much of what you could call flavour chemistry,” said Alan Rocke, a historian at Case Western Reserve University. “There were lots of ideas and anecdotes, but no proper science.”

Yet even with the simplest of reactants, Maillard chemistry was so complicated and produced so many products—hundreds of them—that the research world would largely ignore it until around the time of World War II, Rocke said. That’s when the military became interested in producing on an industrial scale food that both was palatable and had a long shelf life. Because the Maillard reaction is responsible for the appealing aromas of freshly cooked food as well as some of the unwelcome ingredients in processed or long-stored food, scientists began to seriously study the reaction, Rocke explained.

Then in 1953, an African American chemist named John E Hodge, who worked at the U.S. Department of Agriculture in Peoria, Ill, published a paper that established a mechanism for the Maillard reaction (J. Agric. Food Chem.1953, 1, 928).

“Maillard discovered the reaction, but Hodge understood it,” said Vincenzo Fogliano, a food chemist at the University of Naples, Federico II. In fact, because citations of Hodge’s paper far outnumber those of Maillard’s, there has been some discussion of renaming it the Maillard-Hodge reaction, Fogliano said. But that idea hasn’t yet caught on.

According to Hodge’s model, the Maillard reaction has three stages. First, the carbonyl group of a sugar reacts with an amino group on a protein or amino acid to produce water and an unstable glycosylamine. Then, the glycosylamine undergoes Amadori rearrangements to produce a series of aminoketose compounds. Last, a multitude of molecules, including some with flavour, aroma, and colour, are created when the aminoketose compounds undergo a host of further rearrangements, conversions, additions, and polymerizations.

The reaction forms thousands of compounds in food, said Thomas Hofmann, the chair of food chemistry and molecular sensory science at Technical University of Munich. And of those, only a small subset repeatedly contribute to the odour and flavour of cooked food, such as 2,3-butanedione in popcorn and grilled steak.

Over the past several decades, there’s been a huge effort by food scientists to figure out how to influence the end products, Fogliano said. They’ve looked at various starting sugars and proteins as well as how different temperatures, pH levels, moisture levels, and other ingredients affect the creation of desired and undesired odour and flavour products. The idea, he added, is to figure out how to control the unruly Maillard process as it happens in food…..

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